The determination of the positioning of a point in space and the determination of the attitude of an arbitrary object are problems relating to numerous technical fields.
The various solutions generally afforded must resolve any ambiguity in position or attitude, cater for more or less severe dynamics in terms of swing, speeds and accelerations of the systems and satisfy high accuracy, in particular in the aeronautical field.
In systems for detecting position and attitude of objects in space catering for an accuracy of a few millimeters in position and for a degree in attitude, numerous applications exist in various fields.
These systems are used in aeronautics, for the detection of head posture, notably for the helmets for fighter aircraft, for military, civilian or para-civilian helicopters. The latter case of para-civilian application may involve rescue missions at sea for example. They are also used for the detection of simulation helmets, this detection can then be combined with an oculometry device, also called an eyetracker, for detecting the position of the gaze. Numerous applications of these systems also exist in the field of virtual reality and games.
More generally, numerous applications also exist in the field of generic posture detection, notably in the medical field for remote operations and the monitoring of instruments, in the field of position command for slaved machine tools or of remote control and finally for cinema, so as to reproduce movements in synthesis images.
These various applications have technical solutions catering for more or less constraining requirements.
Concerning applications with weak constraints, notably in terms of accuracies, there exist various systems for detecting position and/or orientation of objects.
For example, camera-based devices that recognize patches or shapes use designs printed on an object. Several cameras observe the scene and determine the spatial configuration of the observed design.
There also exist camera-based devices that recognize spheres, which are used, for example in cinema, to reconstruct human movement. The device uses several cameras which observe reflecting spheres and determine their trajectory.
Finally there exist ultrasound positioning devices relying on the principle of triangulation between ultrasonic emitters and receivers.
Concerning higher-performance applications, in particular in the aeronautical field, devices for detecting posture of helmets in aircraft use two principal techniques, namely electromagnetic posture detection and electro-optical posture detection.
Electromagnetic posture detection requires devices comprising means for emitting an electromagnetic field and reception sensors on the helmet making it possible to determine their position with respect to the emitter.
Electro-optical posture detection generally requires patterns of electroluminescent diodes, also called LEDs, disposed on the helmet and several sensors of camera type mounted in the cockpit making it possible to determine the spatial configuration of a pattern of LEDs.
These devices often require several cameras and several sensors. Generally, the computations are complex and the slaving of the detection of the movement of an object requires significant computational resources. This complexity is related to the spatial geometry due to disposition of the sensors on the object and/or large amplitudes of the attitude of the object as well as the swiftness of the movement. The position computations then demand numerous resources and the real time analysis is complex to implement.
To improve performance, other devices comprising sensors of gyroscopic, accelerometric or magnetometric types are frequently combined. This hybridization of sensors makes it possible to improve dynamic performance or to resolve an orientation ambiguity. Nonetheless, the hybridization of the systems adds complexity and bulk.
These solutions therefore exhibit a certain number of drawbacks and limitations, particularly in the aeronautical field.
As regards electromagnetic posture detection devices, robust solutions are difficult to implement.
In particular, in the aeronautical field, stray radiations and electromagnetic disturbances may degrade the performance of the existing systems.
A solution implementing a device of electro-optical type such as described in patent FR 2 905 455 makes it possible to circumvent the drawbacks of the electromagnetic devices.
Moreover, this solution preferably uses image projection means of the video-projector type.
In particular, monochromatic laser video-projectors have the advantages of emitting in a very narrow band of frequencies, a sharp image in a wide field and of making it possible to concentrate a high energy in a very small zone.
A solution of this type is also detailed in the French patent filed under the number 08 05315 on 26 Sep. 2008, in which is described a system for projecting sighting marks onto photosensitive sensors reducing the computations required for detecting the posture of an object in space.
On the other hand this solution exhibits drawbacks of bulkiness, implementation and the stray lights, such as that of the sun illuminating the sensors situated on the moving object may induce detection errors.
More precisely, this solution comprises electro-optical sensors disposed on the object and distributed group-wise.
A drawback of such sensors is the constraint of accuracy of mechanical transfer of the sensors onto their support. Indeed, one typically seeks to obtain accuracies of the order of a milliradian in orientation on linear sensors of a length of the order of 3 cm. This imposes a transfer accuracy of the order 30 μm which must be maintained under all temperature conditions, inter alia. If the sensor is in a plane and possesses a parallelepipedal shape, it must be potentially transferred onto ceramic and necessitates a very specific manufacturing process.
Moreover, this disposition contributes to the compounding of errors of mechanical tolerancing, for example in the positioning of the sensor on the helmet and as regards the accuracy of the sensor. The latter solution requires accurate calibration of the sensor, which may involve the storage of correction coefficients at sensor level so as to be able to attain the desired accuracy level.